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Sanders is "disappointed" in Chelsea Clinton's attack on his health care plan

Hillary Clinton and Sanders will meet Sunday night for fourth debate

(CNN)Bernie Sanders on Sunday rejected the Clinton campaign's assertions that his proposals for single-payer health care would be the undoing of decades of progressive programs and reform.

In particular, the Vermont senator said he was "disappointed" in comments from Chelsea Clinton suggesting Sanders' plan would "dismantle" Medicare, Medicaid and Obamacare, stripping "millions and millions and millions of people of their health insurance."

The attack was "not factual," Sanders told CNN's Jake Tapper on "State of the Union," while also defending against accusations he would increase the tax burden on middle class families to fund the new system.

"If you consider a Medicare premium (a) tax," then yes, those would be increased, Sanders said. But he added, "We are eliminating private health insurance premiums (with the single-payer program) so you're not going to have pay any."

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He said this would save most people "thousands of dollars a year."

Asked about reports Clinton's super PAC, "Correct the Record," would be actively seeking his medical records, Sanders said he had always planned to release the information, was in good health, and would offer written evidence of it soon.

"It's not a problem," he told Tapper.

Responding to the Clinton campaign's steady criticism of his past gun control positions, the senator said he "resented" the suggestion he was in the National Rifle Association's back pocket.

On Saturday though, Sanders announced he would support legislation to roll back 2005 law granting firearm manufacturers legal immunity, a bill he supported a decade ago.

"There were provisions in that legislation" -- like one that banned a particularly deadly brand of bullets -- "that made sense to me," he said.

Sanders and Clinton will meet later Sunday night for the fourth debate of the Democratic presidential primary race. Polls show the candidates locked in tight battles in early voting states Iowa and New Hampshire, but Clinton holds a large lead in national polling.